The present invention relates to an insulating material composed of a non-single crystalline silicon compound including argon atom.
In this specification and Claims, the wording "non-single crystalline" means amorphous, micro crystalline or poly crystalline.
In a fabrication of a solar cell, there hitherto has been widely used a ITO/glass substrate or SnO.sub.2 /glass substrate with a transparent conducting film such as ITO (indium tin oxide) or SnO.sub.2 being formed on a light-transparent substrate, and also a metal substrate such as a stainless steel, iron, aluminum, nickel, brass, copper, zinc or an alloy thereof, or a metal which is surface-treated with another metal.
In case that a conducting substrate such as a metal substrate is used for a substrate of a solar cell, the substrate and the lower electrode of the solar cell which is placed on the substrate must be electrically insulated from each other. This is because a plurality of cells is patterned and formed on a single substrate, and those cells are connected to each other in series. Therefore, an insulator is provided on a conducting substrate for this purpose. As a material of such an insulator, it is needed that the material is heat-resistant because a fabricating process of a solar cell essentially includes a process wherein a temperature of substrate reaches about 200.degree. to 350.degree. C. Therefore, a heat-resistant organic high polymer material, such as an imide resin is generally applied to a substrate by spin coating or dipping method, and heat-treated for the purpose of curing, degassing, and the like.
In general, the higher a film-forming temperature of a solar cell is, the better quality of the solar cell can be obtained. However, in case that a solar cell is fabricated by use of a substrate on which an insulator layer of imide resin or the like is provided as mentioned above, the temperature of the substrate is limited at most to 250.degree. C., hence a solar cell of good quality cannot be obtained. In addition, a condensation occurs in the insulator layer while the substrate is heated and as a result, H.sub.2 O or other impurities will be released, so that a quality of the solar cell might be further reduced. There is also proposed an insulating material wherein the insulation is realized by use of a non-single crystalline silicon. In that case, a limit of a voltage per unit thickness beyond which a dielectric breakdown occurs (hereinafter referred to as "breakdown voltage") is as low as 20 to 30 V/.mu.m, hence the insulator layer must be deposited thick.
An object of the present invention is to provide an insulating material in which the insulation property and heat-resistant property are both fairly good as compared with the coventional insulating material composed of polymer material, non-single crystalline silicon, or the like.
This and other objects of the invention will become apparent from the description hereinafter.